Downhole leak detection

Abstract

A leak detection tool is positioned in in a tubing string that is disposed in a wellbore. The leak detection tool is attached to a downhole end of a line and includes a cup. An outside diameter of the cup is substantially the same as an inside diameter of the tubing string. An uphole end of the line is attached to a spool disposed proximate to an uphole end of the wellbore. The leak detection tool is propelled through the tubing string in a downhole direction by pumping a fluid down the tubing string such that a fluid pressure uphole of the cup is greater than a fluid pressure downhole of the cup. A flow of fluid from an interior of the tubing string uphole of the cup to an exterior of the tubing string through a leak in a wall of the tubing string is detected as the cup passes the leak. A depth of the leak is determined based on a length of the line from the spool to the leak detection tool when the flow of fluid from uphole of the cup through the leak is first detected.

The invention claimed is: 
     
       1. A method comprising:
 positioning a leak detection tool in a tubing string disposed in a wellbore, the leak detection tool attached to a downhole end of a line and comprising a cup, wherein an outside diameter of the cup is substantially the same as an inside diameter of the tubing string and wherein an uphole end of the line is attached to a spool disposed proximate to an uphole end of the wellbore, and wherein the leak detection tool further comprises a circulation port configured to selectively allow fluid to flow from uphole of the cup to downhole of the cup; 
 propelling the leak detection tool through the tubing string in a downhole direction by pumping a fluid down the tubing string such that a fluid pressure uphole of the cup is greater than a fluid pressure downhole of the cup, wherein the circulation port is closed as the leak detection tool is propelled in the downhole direction; 
 detecting a flow of the fluid from an interior of the tubing string uphole of the cup to an exterior of the tubing string through a leak in a wall of the tubing string as the cup passes the leak; 
 determining a depth of the leak based on a length of the line from the spool to the leak detection tool when the flow of fluid from uphole of the cup through the leak is first detected; 
 opening the circulation port after the depth of the leak is detected; and 
 pulling the leak detection tool in an uphole direction with the line. 
 
     
     
       2. The method of  claim 1 , wherein detecting the flow of the fluid from uphole of the cup through the leak comprises detecting a change in fluid pressure in the interior of the tubing string uphole of the cup. 
     
     
       3. The method of  claim 1 , wherein detecting the flow of the fluid from uphole of the cup through the leak comprises detecting a change in the temperature of fluid flowing in the interior of the tubing string uphole of the cup. 
     
     
       4. The method of  claim 1 , wherein detecting the flow of the fluid from uphole of the cup through the leak comprises detecting a change in a pump rate of the pumping. 
     
     
       5. The method of  claim 1 , wherein detecting the flow of the fluid from uphole of the cup through the leak comprises detecting a change in a weight on the line. 
     
     
       6. The method of  claim 1 , wherein the line is a slickline. 
     
     
       7. The method of  claim 1 , wherein the cup is an elastomer cup. 
     
     
       8. The method of  claim 1 , wherein the fluid is pumped at a substantially constant rate. 
     
     
       9. A system comprising:
 a leak detection tool disposed in a tubing string in a wellbore, the leak detection tool comprising:
 a cup, wherein an outside diameter of the cup is substantially the same as an inside diameter of the tubing string, 
 a circulation port configured to selectively allow fluid to flow from uphole of the cup to downhole of the cup; and 
 a sensor unit disposed on the tool uphole of the cup and comprising one or more sensors; and 
 a jar-activated shear pin operable to open the circulation port; 
 
 a line having an uphole end and a downhole end, wherein the uphole end is attached to a spool disposed proximate to an uphole end of the wellbore and the downhole end is attached to the leak detection tool; and 
 a pump to pump fluid into the tubing string uphole of the leak detection tool and thereby propel the leak detection tool through the tubing string in a downhole direction and past a leak in the tubing string. 
 
     
     
       10. The system of  claim 9 , wherein the sensor unit comprises a pressure sensor configured to measure a pressure of the fluid in an interior of the tubing string uphole of the leak detection tool. 
     
     
       11. The system of  claim 9 , wherein the sensor unit comprises a temperature sensor configured to measure a temperature of fluid flowing in the interior of the tubing string uphole of the cup in an exterior of the tubing string. 
     
     
       12. The system of  claim 9 , further comprising a line weight sensor configured to measure the weight of the line and leak detection tool as the leak detection tool is propelled downhole. 
     
     
       13. The system of  claim 9 , wherein the line is a slickline. 
     
     
       14. The system of  claim 9 , wherein the cup is an elastomer cup. 
     
     
       15. The system of  claim 9 , wherein the leak detection tool further comprises a mandrel attached to the cup, and wherein the line is attached to an uphole end of the mandrel.